The present invention relates to a process and apparatus for inserting a rigid support within a contractible sleeve for covering a joint between electric cables, said apparatus being of the type which comprises a device arranged to engage a sleeve for fixing its positioning in axial direction and an actuator arranged to engage a rigid support having an outer diameter greater than the unstretched inner diameter of the sleeve and which is to be coaxially inserted in the sleeve by applying on the support itself an advancing force directed in axial direction.
As is known, in a joint, the connections between the conductors of electric cables usually are enclosed within sleeves which can be fundamentally classified in two classes: sleeves of heat-shrinkable material and sleeves of elastomeric material. For installation purposes, both types of said sleeves must be applied on rigid supports, generally of cylindrical tubular configuration and having an outer diameter greater than the unstretched inner diameter of the corresponding sleeve.
When the sleeve is of the heat-shrinkable type, its application takes place by previously heating the sleeve itself. After the sleeve has cooled, it will maintain its dimension even when it is removed from the support. Then, the sleeve per se is subjected to flame heating causing it to shrink and tending to return it to the original dimensions.
In the case of sleeves of elastomeric material, their application to the support is carried out through the forced insertion of the support into the sleeve and consequent elastic expansion of the sleeve. Consequently, the sleeve will tend to assume its original dimensions as soon as it is removed from the support.
The described operations mainly have the purpose of causing an expansion of the sleeve in the radial direction to allow an easy application of the sleeve over one of the cables before effecting the connection of the cables. When the conductors of the cables have been mutually interconnected, the sleeve is positioned on the joining zone and is caused to shrink (such as by heating the heat-shrinkable sleeves or by merely removing the support from the elastomeric sleeves) and to grip the surfaces of the insulations of the cables.
It is found that the apparatus used at the present time for applying the sleeves, either of heat-shrinkable type or of the elastomeric type, on the respective supports substantially comprises an actuator acting on the rigid support to insert it within the sleeve starting from a first end of the sleeve, and a device which engages the sleeve in proximity of its second end for fixing its positioning in the axial direction and reacting to the axial force which causes the translation of the support.
It has been found that the use of the conventional apparatus leads easily to a series of drawbacks deriving substantially from the fact that the sleeve tends, undesirably, to shorten during the insertion of the rigid support. Moreover, it has to be considered that often the sleeves of this type have a considerable length with respect to the cross-section thereof, and the result is, therefore, that the sleeve is very sensitive to the buckling loads applied on them during the application operation.
As a result, the length of the sleeves applied on the supports is considerably less than the original length of the sleeves before application to the support, and the sleeves can suffer damage due to possible foldings that a buckling load can cause. It is easy to understand that this situation can compromise the reliability of the sleeves, and therefore, the reliability of the joints of cables formed therewith since the sleeve may be deformed in its structure, or the pressure exerted by it on the surfaces of the cables can be distributed irregularly.
In addition to the above, it is found that, to limit as much as possible the described drawbacks, it is necessary that the insertion of the support within the sleeve be made very slowly with a consequent reduction of the productivity.